Some ebook publishers are willing to publish in multiple formats. We have Adobe (PDF), BBeB (LRX), eReader (PDB), and Mobipocket (PRC) with books in all of the mentioned formats. So yes, some publisher will do this to get their product out toe the masses.
As for best seller lists, do we want an ebook only list or a combined list? Me, I'd favor having three lists. One for ebooks, pbooks, and combined. I'd love to see what sort of difference ebooks make to the pbook best seller lists.